With the progress of the antenna technology, the size of the antenna grows smaller and smaller. Generally speaking, the quality and strength of the signal received by the antenna are more or less relevant to the size of the antenna. In particular, for antenna for sensing an active state of an object, the quality and strength of the signal received by the antenna are critical to the degree of sensing accuracy.
Therefore, in general, if the quality and strength of the signal received by the antenna are to be improved, the size of the antenna usually has to be enlarged.